GB2090635A

GB2090635A - Arrangement for the automatic adjustment of clearances in drum brakes

Info

Publication number: GB2090635A
Application number: GB8135080A
Authority: GB
Original assignee: Nissin Kogyo Co Ltd
Current assignee: Nissin Kogyo Co Ltd
Priority date: 1980-11-20
Filing date: 1981-11-20
Publication date: 1982-07-14
Also published as: US4480726A; GB2090635B

Description

1 GB 2 090 635 A 1

SPECIFICATION Arrangement for the Automatic Adjustment of Clearances in Drum Brakes

The present invention relates to an arrangement for automatically adjusting the 70 clearance or braking gap in a drum brake of the type in which, for braking, a pair of brake shoes is expanded into engagement with the inside face of the brake drum.

In a conventional braking gap adjuster 75 arrangement of this type, the braking gap is adjusted by rotating and adjusting gear by means of an adjusting lever, thereby to cause extension of an adjusting member. During braking, however, rotation or returning of the brake lever, and hence 80 adjustment of the braking gap, undergo variations, i.e., are set to too large magnitudes due to compressive deformation of the linings, overall deformation of the brake shoes, etc, resulting in generation of rattles, and dragging or binding of the linings. In addition, violent turning of the brake lever exerts an over- load on the adjusting lever, which may damage, or impair the operation of, the adjusting lever.

It is an object of the invention to provide an automatic braking gap adjustment arrangement suitable for use with a drum brake of the aforesaid type, which effectively avoids or significantly reduces excessive adjustment of the braking gap and prevents application of an over-load to the adjusting lever so as to prevent it from being damaged or impaired.

According to the invention, there is provided an arrangement for the automatic adjustrnent of a braking gap or clearance in drum brake of the type in which a pair of brake shoes is expanded into engagement with the inside face of a brake drum, comprising, in combination, a brake lever which, at or adjacent one end, abuts one brake shoe to cause expansion of said shoe, a support shaft which extends generally at a right angle to said brake lever and includes a portion which is tapered in the axial direction of the support shaft, and adjusting lever which is loosely fitted over said support shaft and, at or adjacent one end, abuts a face at or adjacent one end of said brake [ever, and is pawl-shaped at or adjacent its other end, an adjusting gear rotatable to effect extension of an adjusting member, said gear engaging with the other pawl-shaped end of said adjusting lever, and a compression spring acting between said support shaft and the said adjusting lever, the spring applying a predetermined load to said adjusting lever to bias the latter toward said brake lever and urge it against the tapered face of said support shaft.

Another object of the invention is to provide an automatic braking gap adjuster arrangement for a drum brake of the aforesaid type, which reduces dimensional variations as much as possible in a state where the pawl of the adjusting lever is in engagement with the adjusting gear, whereby adjustment of the braking gap is effected stably and surely, and places a limitation on the retraction of the brake lever in its inoperative direction.

According to a further aspect of the invention, this object is achieved by the provision of an arrangement of the aforesaid type in which the support shaft to which the brake lever is secured is rotatably mounted relative to a substantially Ushaped sliding block, which is mounted on a back plate for sliding movement generally in the direction of expansion of the brake shoes, and which supports the adjusting member in an extensible manner, and in which,part of the side walls of the said sliding block is inwardly bent to form a stop portion, upon which the inoperative side of the brake lever abuts, said stop portion placing a limitation on the retraction of the brake lever in its inoperative direction. According to this aspect of the invention, it is possible to limit the amount of retraction of the brake lever in its operative direction with ease and sureness, but without recourse to any special stop member. This reduces the number of parts and facilitates assembly. In other words, it is possible to reduce tplerances, clearances or allowances that increase with an increase in the number of parts and, hence, prevent more effectively dimensional variations which occur when the pawl of the adjusting lever is in engagement with the adjusting gear.

A further object of the present invention is to provide an automatic braking gap adjuster arrangement which, in braking, conveys the rotational force of the brake lever to the adjusting lever without causing a loss of strokes, thus assuring stable and positive adjustment of the braking gap.

According to another aspect of the invention, this object is achieved by the provision of an arrangement of the aforesaid type, in which the adjusting lever is constantly urged against the brake lever by means of a spring member acting between both levers.

In order that the present invention may be more readily understood, reference will now be made to the accompanying drawings, in which:- Fig. 1 is a front view of one embodiment of the invention, which is applied to a drum brake of the type in which, under braking, one brake shoe is urged against the drum, whereafter the other brake shoe is urged against the drum by the resulting reaction force; Fig. 2 is a sectional view taken along the line 11-11 of Fig. 1; Fig. 3 is a sectional view taken along the line 111-111 of Fig. 1; Fig. 4 is a front view of the salient parts of another embodiment of the invention, which is applied to a drum brake of the type in which, under braking, a pair of brake shoes are urged against the drum by means of a wheel cylinder; Fig. 5 is a sectional view taken along the line V-V of Fig. 4; Fig. 6 is a perspective view of the adjusting lever used in the embodiment of Figs. 4 and 5; Fig. 7 is a front view of the salient parts of a GB 2 090 635 A 2 further embodiment of the invention, in which stop portions are formed on the sliding block of the drum brake illustrated in Fig. 1, and the brake lever is urged against the adjusting lever by a spring member; and Fig. 8 is a sectional view taken along the line VIII-Vill of Fig. 7.

Referring to the embodiment shown in Figs. 1 to 3, a pair of brake shoes 2 carries a back plate 1 which, in use, is fixed to a stationary part of a 75 vehicle body.

A generally U-shaped sliding block 3 is disposed between adjacent ends of the two brake shoes 2. A rattle-preventing spring 6 is interposed between a fixed plate 4 which abuts the sliding block 3 and a slide plate 5, the back plate 1 being held in place between the slide plate 5 and a set plate 7 by means of a clamp bolt 8. The sliding block 3 can thus be slid on the back plate 1 in the general direction in which the said adjacent ends of the brake shoes 2 move away from each other under braking, i.e., in the direction of expansion of the shoes.

Threadedly coupled to the sliding block 3 is an adjusting member 9 which includes a slotted head 9a in which is fitted the web 2a at the said adjacent end of the trailing shoe, the adjusting member 9 being extensible in response to rotation of an internally threaded adjusting gear 10. A brake lever 11 is disposed between the opposed side walls 3a of an opening in the sliding block 3 with gaps C (Fig. 3) being provided between the brake lever 11 and side walls 3a. A support shaft 12 extends through the brake lever 11, and is provided with a serrated orsplined portion 12a which locks the shaft 12 to the lever 11. The un-serrated or smooth portion 12b of the shaft 12 on opposite sides of the serrated portion 12a rotatably engage in a pair of notches 3b in the side walls of the sliding block-3. An intermediate region of an end face 11 a of the brake lever 11 abuts the web 2a at said adjacent end of the leading shoe.

An adjusting lever 13 is provided for rotating the adjusting gear 10, and includes a depressed portion 13a (Fig. 3) formed with an opening 13b of larger diameter than that of the support shaft 12, in which the support shaft 12 is loosely inserted. The adjusting lever 13 has one upper end 13c (as viewed in Fig. 2) abutting the upper region of the end face 11 a of the brake lever 11 located on the leading side of the latter, and the other end 13d is shaped or otherwise formed or provided with a paw] engaging with the external teeth of the adjusting gear 10. It is to be noted that the adjusting lever 13 could alternatively be arranged in such a manner that, as viewed in Fig.

2, a lower end thereof abuts the lower region of the end face of the brake lever 11 (i.e. a region below the shaft 12) located on the trailing side of the lever 11.

A spring guide 14 is fixed, for example pressed or force-fitted onto, the serrated head 12c of the support shaft 12. A compression spring 15, both ends 15a of which are polished, is disposed 130 between a stop portion 14b of the guide 14 and the depressed portion 13a of the lever 13, extending along and overlying the guide portion 14a of the guide 14. A predetermined load is applied by the compression spring to the adjusting lever 13 to bias the latter towards the brake lever 11 so that the opening 13b in the adjusting lever 13 is urged against an intermediate frusto-conical portion or seat 12dof the support shaft 12, which portion tapers down in a direction towards the head 12c.

A gaiter or dust boot 16 (Fig. 2) is provided, with its edge clamped to the back plate 1. A return spring 17 (Fig. 1) is provided between the brake shoes 2 in the vicinity of the sliding block 3, and an anchor spring 18 is provided between the brake shoes 2 in the vicinity of an anchor 19. The operation of the illustrated arrangement will now be described. 85 When the brake lever 11 is pivoted in an anticlockwise direction as indicated by the arrow in Fig. 2 by pulling a brake cable or wire (not shown) connected to the brake lever 11, the brake shoe 2 located on the leading side, i.e. the leading or left- hand brake shoe, is expanded to urge its lining 2b against the inner surface or a brake drum. The resulting reaction force causes the sliding block 3 to slide to the right on the back plate 1, and thereby causes the trailing or right hand brake 9.5 shoe 2 to expand, so that its lining 2b is urged against the opposite inner surface of the brake drum to effect braking.

In this case, the adjusting lever 13 pivots in an anti-clockwise direction with the brake lever 11 due to the cooperation of the end 1 3c of the lever 13 with the upper end face 11 a of the lever 11. However, provided that the pivotal movement of the lever 11, and therefore of the the lever 13, is relatively small, no rotation of the adjusting gear 10 will take place due, to the fact that play occurs between the pawl- shaped end 1 3d of the adjusting lever 13 and the teeth of the adjusting gear 10. When the lever 11 is released and & lowed to turn clockwise, under the action, primarily, of the spring 17, the lever 13 follows due to the frictional engagement of the depressed lever 13a with the tapered shaft portion 12d, since the shaft 12 is locked to the lever 11.

As the abrasion losses of the linkages 2b reach or exceed a given amount due to repeated braking, the amount of pivotal movement of the brake lever 11 increases with attendant increases in the amount of pivotal movement of the adjusting lever 13. This results in the elimination or take up of ail the play between the pawlshaped end 13dand the teeth of the adjusting gear 10, and hence rotation of the latter occurs. The adjusting member 9 is thereby extended relative to the block 3 by a distance substantially corresponding to the abrasion losses of the two linings 2b, so that the braking gap or clearance is always kept substantially constant in an automatic manner.

As will be apparent from Figs. 1 and 3, the upper end 13c of the adjusting lever 13 which is 2 1 7 1 3 GB 2 090 635 A 3 engaged by the upper end face 11 a of the brake lever 11 is offset axially of the support shaft 12 relative to the mounting of the adjusting [ever 13 by means of its depressed portion 13a on the tapered portion 12d of the shaft. Therefore, when the brake [ever 11 is rotated anti- clockwise, in addition to urging the adjusting lever 13 in an anti- clockwise direction, it will exert a turning couple on the lever 13 tending to rock it in an anti-clockwise direction as viewed in Fig. 1, and tending to urge the pawl-shaped end 13dfurther into engagement with the teeth of the adjusting gear 10. The resultant reaction tends to draw the brake lever 11 and shaft 12 axially downwardly as viewed in Fig. 3, so as to at least partially take up the clearance C on the lowermost side of the lever 11.

When after brake application and rotation of the adjusting gear 10 as previously explained, the brake lever 11 is released and pivots in a clockwise direction as viewed in Fig. 2, the aforementioned turning couple is noplonger applied to the adjusting lever 13, and this, together with the said take up of the lowermost clearance C, and/or because of the relative configurations of the gear teeth and pawl, facilitates or enables the pawlshaped end 13dof the adjusting lever 13 to advance over one tooth of the adjusting gear 10 to the next one when the lever 11 is released, whereby the adjusting lever 13 returns to its normal position without any significant slippage between the depressed portion 13a and the tapered shaft portion 12d. The return of the lever 13 to its normal position can take place surely and smoothly without causing any reverse rotation of the gear 10, since the gaps C and C between the brake lever 11 and the side walls 3a and 3a of the opening in the sliding block 3 provide for retreat for the lever 13.

In the automatic adjustment of the braking gap 105 which takes place during braking, the linings 2b may undergo compressive deformation, the brake drum and other parts may suffer thermal deformation, and the brake shoes 2, overall, may experience deformation. When the braking gap or 110 clearance is reduced to zero due to such deformation and, thereafter a pivotal force is applied to the brake lever 11, due to the previously-mentioned turning couple caused by 50. the axial offset between the upper end face 13c and the depressed portion 1 3a, the adjusting lever 13 will be swung aside in the direction of the arrow atA in Fig. 3 about the pawl-shaped end 13d, and will move bodily towards the leading side (to the left as viewed in Fig. 1) by a distance corresponding to the space between the opening 13b and the support shaft 12, so that the edge of the opening 13b located on the trailing side slides down and abuts the tapered portion or face 12d, while the edge of the opening 13b on the leading ide is separated from the tapered portion 12d. Therefore, the rotational force of the shaft 12 exerted by the pivotal movement of the brake lever 11 is not transmitted to the adjusting lever 13, assuring that neither over-adjustment of the braking gap nor application of an excessive load on the lever 13 occurs. When the pivotal force is then removed from the brake lever 11, the adjusting lever 13 is positively restored to its original position on the tapered portion 12d along the guide portion 14a of the spring guide 14, due to the restoring force exerted by the compression spring 14, without the lever 13 changing direction, i.e. without changing its angular orientation.

In the embodiment of Figs. 4 to 6, the back plate 1 is fixedly provided with an hydraulic wheel cylinder 2 1, and the adjacent ends of the webs 2a of the brake shoes 2 engage in slots in the outer ends 22 of associated pistons 22 of the cylinder 2 1. The support shaft 12 is anchored to a parking brake lever 23 so as to be positioned at right angles with the plane of the lever. In the vicinity of the wheel cylinder 21, there is provided an adjusting member 9 formed by telescopically inserting one end of a first strut 24,nto the adjacent end of a second strut 25, said first strut having its outside threaded at 24a. The support shaft 12 is rotatably supported on the opposite or outer end of the first strut 24. The opposite outer end of the second strut 25 abuts the web 2a of the trailing shoe. An adjusting nut 26 is screwed onto the threaded portion 24a of the first strut 24, and abuts upon the end face of the opening in the second strut 25. Turning of the adjusting nut 26 causes the first strut 24 to be extended relative to the second strut 25, whereby the brake shoes 2 are moved away from each other to adjust the braking gap.

The adjusting [ever 13 is loosely fitted over the support shaft 12, which passes through the opening 13b which is of larger diameter than that of the shaft 12. The peripheral edge of the opening 13b is depressed at 13a in a direction towards the parking brake lever 23. The adjusting lever 13 is pivotally supported by causing the depressed portion 13a to abut the tapered face or portion 12dof the support shaft 12. One end of the adjusting lever 13, i.e. its upper end 1 3c, abuts one end face of the parking brake lever 23 located on the leading side thereof. The other pawl-shaped end 13dof the lever 13 engages with external ratchet teeth on the adjusting nut 26.

Operation of this illustrated arrangement will now be described.

A pressurized liquid is fed to the wheel cylinder 21 by actuation of a master cyclinder (not shown). This displaces the pistons 22 and expands the brake shoes 2, so that the associated linings 2b and 2b contact the inner face of the brake drum for braking. To apply the parking brakes, the parking brake lever 23 is pivoted in the anti- clockwise direction indicated by an arrow in Fig. 5. Such pivotal movement firstly causes expansion of the leading brake shoe (the left-hand shoe as viewed in Fig. 4), and causes its lining 2b to be urged against the brake drum. The resulting reaction force causes the trailing brake shoe 2 to be pushed and expanded by the first 4 GB 2 090 635 A 4 and second struts 24 and 25. The associated lining 2b is then urged against the opposite side of the brake drum for braking.

When the abrasion losses of the linings 2b reach a giver value, the amount of pivotal movement of the parking brake lever 23 increases 70 with attendant increases in the amount of pivotal movement of the adjusting lever 13, resulting in turning of the adjusting nut 26. Turning of the adjusting nut 26 causes the first strut 24 to be extended from the second strut 25 by a distance corresponding to the abrasion losses of the linings 2b. In this way, the automatic adjustment of the braking gap is accomplished.

is Referring to Figs. 7 and 8, there is shown a further embodiment of the invention.

According to this embodiment, a pair of stop members or portions 3c are formed by inwardly bending the upper portions ot side walls 3a and 3a which bound an opening in a sliding block 3. An end face 11 b positioned on the inoperative side of the brake lever 11 abuts the stop portions 3c, thus limiting retraction of the brake lever 11 in its retraction (clockwise) direction.

The limitation of the retractive movement of the brake lever 11 in its inoperative direction is then set when the brake lever 11 is rotatably engaged with the sliding block 3, and this block is slidingly mounted on the back plate 1 by a clamp bolt 8. This renders it possible to reduce 95 considerably the variation in or extent of the movement of the paw] or paw[-shaped end 13d of the adjusting lever 13 in the state in which the pawl is in engagement with the adjusting gear 10.

It should be noted that the above-mentioned stops 3c may be formed not only on the upper portions of the side walls 3a of the opening but also or alternatively on the lower portions thereof.

If a distance 11 (Fig. 8) separates the point at which the stops 3c of the sliding block 3 abut the inoperative end face of the brake lever 11 and the central point of the support shaft 23, and if this distance is increased and approaches a distance'2 (Fig, 7) which separates the paw[ 13d of the adjusting lever 13 and the central point of the support shaft 12, then it is possible to maximise the reduction in variations in the movement of the pawl 13d in the state in which it is in engagement with the adjusting gear 10.

As shown in Fig. 7, a spring member 31 is 115 provided which has an intermediate portion 3 1 a inserted through a holding slot 13e in the adjusting lever 13. As also shown in Fig. 8, this spring member then passes below the upper face 13fof the adjusting lever 13, and is locked atone end 3 1 b in a locking groove 11 c formed on the upper portion of the inoperative end face 11 b of the brake lever 11. The spring member also passes above the upper face 1 3f, and is locked at its other end 31 c, in a locking groove 13g formed in the edge of the face 13f of the adjusting lever 13 remote from the end of the brake lever 11. Since the spring member is thus disposed across both levers 11 and 13, the adjusting lever 13 is constantly urged against the operative end face 11 a of the brake [ever 11.

As a result, since the rotational force of the brake [ever 11 is conveyed to the adjusting lever 13 without causing a loss of strokes, constant and stable adjustment of the braking gap is ensured. In addition, since the spring member 31 has its intermediate portion 31 a inserted through the holding slot 13e in the adjusting lever 13, and is disposed across both lever 11 and 13, it is possible to positively urge the adjusting lever 13 against the brake lever 11. Thus, the arrangement according to this embodiment can be used for a longer period of time with not risk of its disengagement.

With the arrangement which, as mentioned herein, comprises a brake lever which abuts at its one end upon one brake shoe to cause expansion of said shoe, a support shaft which extends at right angles with respect to said brake [ever and includes a portion tapered in the direction in which it extends, an adjusting lever which is loosely fitted over said support shaft and has one end abutting one end face of said brake lever, an adjusting gear for permitting extension of an adjusting member, said gear engaging with the other pawl-shaped end of said adjusting [ever, and a compression spring interposed between an extended head of said support shaft and the said adjusting [ever, a predetermined load applied to said spring causing said adjusting lever to be biassed toward said brake lever and urged against the tapered face of said support shaft, transmission of the rotational force of the brake lever to the adjusting lever is assured. This causes extension of the adjusting member, so that adjustment of the braking gap is automatically ensured, and effected smoothly. Even when an excessive rotational force is applied to the brake [ever, the adjusting lever fitted over the support shaft is moved away from the brake lever against the compression spring and is displaced towards one brake shoe. Hence, since the rotational force of the brake lever is not transmitted to the adjusting lever, no rotation of the adjusting gear takes place. Since the adjusting lever then returns smoothly and positively to its original position under the influence of the compressions spring, over-large adjustment of the braking gap is effectively prevented with neither rattles nor dragging of the linings, thus assuring constantly stable braking. In addition, since no excessive load is applied to the braking lever, it is not positively damaged or impaired, so that its use for braking over an extended period of time is assured.

In another arrangement, the brake lever is disposed between the side walls of the opening in the generally U-shaped sliding block, and part of one or both side walls of the latter is inwardly bent to form one or more stop portions. If the inoperative side of the brake lever is permitted to abut upon this stop portion, a limitation can easily and positively be placed on the retraction of the brake [ever in its inoperative direction, when the r, i.

GB 2 090 635 A 5 sliding block is attached to the back plate by means of a clamp bolt. In this way, since the or each stop portion can be formed by bending inwardly part of the block without recourse to any 55 special separate member, there is no increase in the number of parts. This reduces as much as possible dimensional variations in the condition in which the pawl of the adjusting lever is in engagement with the adjusting gear without causing an increase in tolerance or allowance. Thus, adjustment of the braking cap can always be effected with certainty.

If the stop portion of the sliding block is spaced away from the support shaft to place a limitation on the retraction of the brake lever in its inoperative direction, dimensional variations of the pawl of the adjusting lever can be reduced to a lesser extent.

The adjusting lever may be constantly urged against the brake lever by disposing a spring member across both levers. As a result, the rotational force or the brake lever is transmitted in braking to the adjusting lever without causing a loss of strokes, thus assuring more stable and surer adjustment of the braking gap. In addition, the adjusting lever can be positively urged against the brake lever, since the spring member is inserted through the holding slot in the adjusting lever, and disposed across both levers.

Accordingly, the spring member can satisfactorily be used for a prolonged period of time with no risk of disengagement of the components.

Claims

1. An arrangement for the automatic adjustment of a braking gap in a drum brake of the type in which, in operation, a pair of brake shoes is expanded into engagement with the inside face of a brake drum, comprising, in combination, a brake lever which, at or adjacent one end, abuts one brake shoe to actuate said shoe, a support shaft which extends generally at right angles with respect to said brake lever and includes a portion tapered in the axial direction of the shaft, an adjusting lever which is loosely fitted over said support shaft and has one end region abutting one end face or edge region of said brake lever, an adjusting gear for permitting extension of an adjusting member, said gear engaging with a pawl at the other end region of said adjusting lever, and a compression spring acting between the support shaft and adjusting lever, a predetermined load applied on said spring causing said adjusting lever to be biassed toward said brake lever and urged against the tapered face of said support shaft.

2. The arrangement as claimed in claim 1, in which the support shaft to which the said brake lever is secured is rotatably mounted on a generally U-shaped sliding block which is mounted on a back plate for sliding movement in the general direction of expansion of the brake shoes, and which supports the adjusting member in an extensible manner.

3. The arrangement as claimed in claim 1, in which the support shaft to which the said brake lever is secured is rotatably mounted on the adjusting member, the adjusting member comprising two mutually extensible elements, which are provided in the vicinity of a wheel cylinder for causing expansion of the brake shoes, the obter end cif the element abut-Ling one of the brake shoes and the outer end region of the other element mounting the support shaft.

4. The arrangement as claimed in claim 2, in which part of at least one side wall of the said sliding block is inwardly bent to form a stop portion, against which the inoperative side of the brake lever is arranged to abut.

5. The arrangement as claimed in any preceding claim, in which the said adjusting lever is constantly urged against the said brake lever by coupling both levers by a spring member.

6. The arrangement as claimed in claim 5, in which the said spring member has an intermediate portion inserted in a holding slot formed in the adjusting lever, the spring member cooperating at one end with the adjusting lever and at its other end with the brake lever.

7. An arrangement for the automatic adjusting of a braking gap in a drum brake, substantially as hereinbefore described with reference to Figs. 1 to 3 of the accompanying drawings.

8. An arrangement for the automatic adjusting of a braking gap in a drum brake, substantially as hereinbefore described with reference to Figs 4 to 6 of the accompanying drawings.

9. An arrangement for the automatic adjusting of a braking gap in a drum brake, substantially as hereinbefore described with reference to Figs. 7 100 and 8 of the accompanying drawings.

10. A braking system incorporating drum brakes fitted with clearance adjustment arrangements as claimed in any preceding claim.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1982. Published bythe Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.